Ceramic Component

The present disclosure relates to a ceramic component, and it specifically relates to a ceramic component including a ceramic body.

Ceramic components, such as varistors, are used in electronics and electronic devices. Varistors are used for protecting electronics and electronic devices from abnormal voltages caused by lightning surge or static electricity to prevent malfunction of electronics and electronic devices due to noise generated in circuits.

Japanese Patent Laid-Open Publication No. 2020-096075 discloses a chip varistor. This chip varistor includes a body having a laminated structure, first and second conductors extending inside the body, a third conductor located between the first conductor and the second conductor and extending to form first and second functional layers, first, second, and third electrodes connected to the conductors, respectively, and an alkali metal-containing portion that is a portion of the body containing alkali metal and thus having large electrical resistance. The alkali metal-containing portion constitutes the surface of the body and extends inward from the surface of the body along the interface between the body and each of the conductors. The chip varistor is characterized in that the alkali metal-containing portion does not reach the first functional layer and the second functional layer. In this chip varistor, the electrical resistance is increased due to alkali metal disposed along an entire outer surface of the body.

In conventional ceramic components, when the alkali metal disposed on the entire outer surface of the ceramic body as in the chip varistor disclosed in Japanese Patent Laid-Open Publication No. 2020-096075 may cause migration on the surface of the ceramic body.

A ceramic component according to an aspect of the disclosure includes: a ceramic body having a first end surface and a second end surface opposite to each other in a first direction, a first side surface and a second side surface opposite to each other in a second direction, and a first main surface and a second main surface opposite to each other in a third direction; internal electrodes disposed inside the ceramic body; a first external electrode disposed on the first end surface of the ceramic body and extending from the first end surface of the ceramic body to cover a part of the first side surface; a second external electrode disposed on the second end surface of the ceramic body and extending from the second end surface to cover a part of the first side surface of the ceramic body; and a third external electrode disposed on the first side surface of the ceramic body and extending from the first side surface side to cover a part of the first main surface and a part of the second main surface of the ceramic body. The ceramic body contains particular element that is at least one of alkali metal and alkaline earth metal. A first total concentration of the particular element in a vicinity of the first external electrode in a surface layer of the first side surface of the ceramic body and a vicinity of the second external electrode in the surface layer of the first side surface of the ceramic body is different from a second total concentration of the particular element in a vicinity of the third external electrode in the surface layer of the first side surface of the ceramic body.

The ceramic component according to the disclosure has migration suppressing properties enhanced.

An overview of ceramic componentwill be described below with reference to the drawings. The drawings are schematic views, and the size and thickness ratios of each constituent element in the drawings do not necessarily reflect the actual dimensional ratios.

is a schematic perspective view of ceramic componentaccording to an exemplary embodiment.is a schematic cross-sectional view of ceramic component.is a schematic perspective view of ceramic component.

In the following description, as shown in, an X-axis direction parallel to a longitudinal direction of ceramic bodyis defined as a first direction, a Y-axis direction is defined as a second direction, and a Z-axis direction is defined as a third direction. These directions are merely examples, and are not intended to limit the orientation of ceramic componentin operation.

As a result of extensive research aimed at solving the above problems, inventors have found that the distribution of the concentration of particular element which is at least one of alkali metal and alkaline earth metal corelates to characteristics of the ceramic component, and accomplished the disclosure.

The term “particular element” encompasses alkali metal, such as lithium, sodium, potassium, rubidium, and cesium, and alkaline earth metal, such as beryllium, magnesium, calcium, strontium, and barium. Among them, sodium, potassium, magnesium, and calcium are preferable.

As shown in, ceramic componentaccording to this embodiment includes ceramic body, internal electrodes,, and, and external electrodes, that is, first external electrode, second external electrode, and third external electrode.

Ceramic bodyhas first end surface Sand second end surface Sopposite to each other in the first direction (X-axis direction), first side surface Sand second side surface Sopposite to each other in the second direction (Y-axis direction), and first main surface Sand second main surface Sopposite to each other in the third direction (Z-axis direction).

First external electrodeis disposed on first end surface Sand extends from the first end surface Sto cover a part of first side surface S. Second external electrodeis disposed on second end surface Sand extends from the second end surface Sto cover a part of first side surface S. Third external electrodeis disposed on first side surface Sand extends from the first side surface Sto cover respective parts of first main surface Sand second main surface S.

First external electrodeand second external electrodeare external electrodes disposed on end surfaces Sand Sof ceramic body, respectively, (hereinafter also referred to as end surface electrodes). Third external electrodeis an external electrode disposed on side surface Sof ceramic body(hereinafter also referred to as a side surface electrode).

As shown in, ceramic bodyincludes, as external electrode vicinity regions, first external electrode vicinity Nand second external electrode vicinity Nthat are vicinities of first external electrodeand second external electrode, respectively, which are end surface electrodes. In addition, ceramic bodyfurther includes third external electrode vicinity Nthat is a vicinity of third external electrode, which is a side surface electrode, and fourth external electrode vicinity Nthat is a vicinity of fourth external electrode, which is a side surface electrode. The term “external electrode vicinity” refers to a region of the ceramic body that is within a distance of 50 μm from an end of an external electrode in the first direction (X-axis direction) and is connected to the external electrode.

In ceramic componentaccording to this embodiment, ceramic bodycontains the particular element. A first total concentration of the particular element in first external electrode vicinity Nin surface layerS of first side surface Sand second external electrode vicinity Nin surface layerS is different from a second total concentration of the particular element in third external electrode vicinity Nin surface layerS. In other words, regarding the concentration of the particular element in surface layerS of first side surface Sof ceramic component, the concentration (the first total concentration) in the end surface electrode vicinities is different from the concentration (the second total concentration) in the side surface electrode vicinities.

The “surface layerS” is a region with a depth from the surface is within the detection depth detectable by an Electron Probe Micro Analyzer (EPMA). The EPMA is a measuring apparatus configured to analyze constituent elements based on wavelengths and intensities of characteristic X-rays generated by electron beam irradiation of an object to be measured, and the detectable depth is within a range of 0.1 μm or more and 10 μm or less, preferably within a range of 0.5 μm or more and 2 μm or less, and the depth is more preferably 1 μm.

The “total concentration” of the particular element refers to the whole concentration of the particular element in the external electrode vicinities in surface layerS of first side surface S. The “whole concentration” means a percentage (wt. %) of the whole weight of the particular element contained in a portion of the ceramic body with a certain volume with respect to the weight of the portion of the ceramic body. With respect to the “total concentration”, in the measurement with the EPMA, for example, the percentage of the whole peak area of the particular element with respect to the peak area of elemental Zn of ZnO, which is a main component of the ceramic body, (whole peak area of the particular element×100/peak area of elemental Zn) may be calculated to determine an approximation of the total concentration. The expression “total concentrations are different” means that the first total concentration and the second total concentration are different from each other by 5 wt. % or more.

In ceramic componentaccording to this embodiment, the first total concentration is different from the second total concentration, in other words, the concentration in respective vicinities of the end surface electrodes is different from the concentration in respective vicinities of the side surface electrodes, thereby enhancing the migration suppressing properties. A reason why ceramic componentaccording to this embodiment exhibits this effect as a result of the above configuration may be, for example, that the particular element is provided locally in the external electrode vicinities, or the overall abundance of the particular element is reduced.

In addition, in ceramic componentaccording to this embodiment, as described later, the difference between the concentration in the vicinities of the end surface electrodes and the concentration in the vicinities of the side surface electrodes, the concentration of the particular element in a particular region enhance migration suppressing properties while also enhancing, e.g., sealing properties, plating flow suppressing and properties, moisture resistance.

Ceramic componentaccording to the disclosure includes ceramic body, the internal electrodes, and the external electrodes, that is, first external electrode, second external electrode, and third external electrode. As shown in, ceramic componentincludes fourth external electrodedisposed on second side surface Sand extending from the second side surface Sto cover respective parts of first main surface Sand second main surface S. Third external electrodeand fourth external electrodeinmay be connected to each other on first main surface Sand second main surface Sto extending entirely around ceramic body. Ceramic componentmay further include a plating electrode covering at least part of the surface of each of external electrodes,,, and.

Ceramic componentaccording to the disclosure may be, for example, a varistor, a thermistor, or a ceramic capacitor. As an example, ceramic componentaccording to the disclosure configured to function as varistorwill be described below.

Ceramic bodyof varistoraccording to this embodiment has, for example, a rectangular shape with a long side extending in the first direction (X-axis direction). Ceramic bodyhas dimensions, for example: the length in the first direction (X-axis direction) ranges from 0.6 to 1.6 mm, the length (width) in the second direction (Y-axis direction) ranges from 0.3 to 0.8 mm, and the length (height) in the third direction (Z-axis direction) ranges from 0.3 to 0.8 mm. Corners of ceramic bodymay be chamfered, and the corners of ceramic bodymay be rounded.

In varistor, ceramic bodyis made of, for example, semiconductor ceramic components having non-linear resistance characteristics. Ceramic bodycontains ZnO as a main component, and may further contain, e.g., BiO, CoO, MnO, SbO, PrO, CaCO, or CrOas auxiliary component. In the semiconductor ceramic components, the main component, such as ZnO, is dissolved and sintered with some of auxiliary components, and the remaining auxiliary components are precipitated at grain boundaries, thereby forming ceramic body.

Regarding the concentration of the particular element in surface layerS of first side surface Sof varistorof this embodiment, the first total concentration in first external electrode vicinity Nand second external electrode vicinity Nis different from the second total concentration in third external electrode vicinity N. This configuration provides varistorwith high migration suppressing properties.

The particular element contained in external electrode vicinities N-Nin ceramic bodyhas been diffused from an external electrode paste into ceramic bodyduring, for example, baking for forming the external electrodes during varistorproduction process. Therefore, the first total concentration and the second total concentration of the particular element may be adjusted by, between the end surface electrodes and the side surface electrodes, for example, (1) changing the number of times the external electrode paste is applied or baked; (2) changing the baking temperature or time; or (3) using external electrode pastes having different particular element contents.

Ceramic bodymay include insulating layerR at surface layerS (see). In other words, insulating layerR, that is, a high-resistance region with a layer shape may be formed at surface layerS of ceramic body. In this case, ceramic bodycontains the particular element in surface layerS and has insulating layerR disposed at the surface layer further enhances the migration suppressing properties.

Internal electrodes-are disposed inside ceramic body. The number of the internal electrodes in varistorshown inis, for example, three. Internal electrodeis electrically connected to first external electrode, is an end surface electrode. Internal electrodeis electrically connected to second external electrode, an end surface electrode. Internal electrodeis electrically connected to third external electrodeand fourth external electrode, side surface electrodes.

Internal electrodes-contain metal, such as Ag, Pd, PdAg, or PtAg. Ceramic bodyhaving internal electrodestoinside can be prepared, for example, by applying an internal electrode paste containing the above metal onto ceramic sheets by, e.g., printing, after preparing the ceramic sheets with a ZnO-containing slurry. Then the ceramic sheets with the internal electrode pastes applied thereon are stacked, pressed, and cut. Then, binder in the ceramic sheets is removed at a temperature of, e.g., 300° C. or more and 500° C. or less. Then, the ceramic sheets are baked at a temperature of, e.g., 600° C. or more and 1,100° C. or less.

As shown in, varistorincludes first external electrodeand second external electrodeas end surface electrodes, and third external electrodeand fourth external electrodeas side surface electrodes.

First external electrodeis disposed on first end surface Sand extends from the first end surface Sto cover a part of first side surface S. Second external electrodeis disposed on second end surface Sand extends from the second end surface Sto cover a part of first side surface S. Third external electrodeis disposed on first side surface Sand extends from the first side surface Sto cover a part of first main surface Sand a part of second main surface S. Fourth external electrodeis disposed on second side surface Sand extends from the second side surface Sto cover a part of first main surface Sand a part of second main surface S.

External electrodes,,, andare formed by, for example, applying an external electrode paste containing metal component, such as Ag, AgPd, or AgPt, and glass component, such as BiO, SiO, or BOby, e.g., immersion or printing so as to partially cover end surfaces Sand S, side surfaces Sand S, and main surfaces Sand Sof ceramic body, followed by baking the paste at a temperature of, e.g., 700° C. or more and 800° C. or less.

Plating electrodes,,, andcover at least respective parts of external electrodes,,, and, respectively. Each plating electrode may include, for example, an Ni electrode covering at least a part of each external electrode and an Sn electrode covering at least a part of the Ni electrode. Plating electrodes,,, andare formed by immersing, in a plating solution, ceramic bodyhaving external electrodes,,, andthereon. In a conventional ceramic component, during the formation of a plating electrode, the plating solution may contact a surface of the ceramic body, resulting in so-called plating flow, in which the plating electrode protrudes from the external electrode and spreads onto the surface of ceramic body.

Ceramic component, such as a thermistor or a ceramic capacitor, according to this embodiment other than varistoralso has migration suppressing properties enhanced.

Ceramic componentaccording to first to third exemplary embodiments will be described below.

In ceramic componentaccording to according to the first embodiment, the second total concentration is higher than the first total concentration. In other words, the concentration of the particular element in the vicinities of the side surface electrodes is higher than the concentration in the vicinities of the end surface electrodes. The concentration in the vicinities of the side surface electrodes may become higher than the concentration in the vicinities of the end surface electrodes by: (A) making the concentration (wt. %) of the particular element in the external electrode paste higher in the side surface electrodes than in the end surface electrodes; (B) making the number of times the external electrodes are baked greater in the side surface electrodes than in the end surface electrodes; or (C) making the conditions for baking the external electrodes to be a higher temperature and/or a longer time in the side surface electrodes than in the end surface electrodes, etc.

Ceramic componentaccording to the first embodiment is advantageous in that, in addition to the enhanced migration suppressing properties described above, the sealing properties against the plating solution and flux during mounting are enhanced, and the plating flow suppressing properties is enhanced. In other words, ceramic componentaccording to the first embodiment may also enhance migration suppressing properties, sealing properties, and plating flow suppressing properties.

The effect enhancing sealing properties is due to the following reason, for example: a large amount of glass containing the particular element provided in the vicinity of the side surface electrodes, where sealing properties have been conventionally degraded, enhances the sealing properties against the plating solution, and flux during mounting. In addition, the plating flow suppressing properties is enhanced due to the following reason: a large amount of the particular element with no free electrons provided on the side surface electrodes, where plating flow have conventionally occurred, prevents Ni ions and Sn ions in the plating solution from receiving electrons in the vicinity of the external electrodes.

The second total concentration is preferably 1.2 times or more the first total concentration. This configuration further enhances the migration suppressing properties, sealing properties, and plating flow suppressing properties. The second total concentration is more preferably 1.4 times or more, still more preferably 1.5 times or more, and particularly preferably 1.7 times or more the first total concentration. The upper limit of the second total concentration is not particularly limited, but may be, for example, 3.0 times or less, and preferably 2.0 times or less the first total concentration.

In ceramic componentaccording to a second exemplary embodiment, the first total concentration is higher than the second total concentration. In other words, the concentration of the particular element in the vicinities of the end surface electrodes is higher than the concentration in the vicinities of the side surface electrodes.

Ceramic componentaccording to the second embodiment provides an advantageous effect also enhancing the moisture resistance in addition to the migration suppressing properties described above. In other words, ceramic componentaccording to the second embodiment enhances both of migration suppressing properties and improved moisture resistance.

The enhancing of the moisture resistance is due to the following reason: while a surface insulation degradation during a moisture load test have conventionally occurred at an end surface electrode vicinity serving as the starting point of the reaction, a large amount of glass containing the particular element in the vicinities of end surface electrodes protect the starting point of the surface degradation.

The first total concentration is preferably 1.2 times or more the second total concentration. This configuration further enhances the migration suppressing properties and moisture resistance. The first total concentration is more preferably 1.4 times or more, still more preferably 1.5 times or more, and particularly preferably 1.7 times or more the second total concentration. The upper limit of the first total concentration is not particularly limited, but may be, for example, 3.0 times or less, and preferably 2.0 times or less the second total concentration.

In ceramic componentaccording to a third exemplary embodiment, ceramic bodyincludes particular ridge portion NRand particular ridge portion NR. Particular ridge portion NRincludes ridge Rbetween first side surface Sand first main surface S. Particular ridge portion NRincludes ridge Rbetween first side surface Sand second main surface S. In ceramic componentaccording to the third embodiment, the total concentration of the particular element in particular ridge portions NRand NRis higher than the total concentration of the particular element in surface layerS of first side surface S. In other words, in ceramic componentaccording to the third embodiment, the concentration of the particular element in the ridge portion (particular ridge portion NR) between first side surface Sand first main surface Sin ceramic bodyand the ridge portion (particular ridge portion NR) between first side surface Sand second main surface Sin ceramic bodyis higher than the concentration in entire surface layerS of first side surface S. The particular ridge portions are: a region of ceramic bodythat is within 50 μm from ridge Rconnecting first side surface Sto first main surface Sand that is connected to ridge Rforming surface layerS; and a region of ceramic bodythat is within 50 μm from ridge Rconnecting first side surface Sto second main surface Sand that is connected to ridge Rforming surface layerS. Similar to first side surface S, ceramic bodyincludes a particular ridge portion including a ridge between second side surface Sand first main surface S, and further includes a particular ridge portion including a ridge between second side surface Sand second main surface S. The total concentration in these particular ridge portions is higher than the total concentration of the particular element in surface layerS of second side surface S.

Ceramic componentaccording to the third embodiment provides an advantageous effect enhancing the plating flow suppressing properties in addition to the migration suppressing properties described above. In other words, ceramic componentaccording to of the third embodiment enhances both of migration suppressing properties and improved plating flow suppressing properties.

The effect enhancing migration suppressing properties and plating flow suppressing properties is due to the following reason, for example: while migration have conventionally occurred on the body surface and plating flow have been conventionally occurred at ridge portions of the body, a large amount of the particular element on the ridge portions provide this effect.

The disclosure will be described below with reference to examples, but the disclosure is not limited to the examples.

A ceramic body containing ZnO as a main component was formed, and insulating layerR made of SiOwas formed as surface layerS of the ceramic body. Subsequently, an external electrode paste was applied to a surface of insulating layerR and baked, thereby producing ceramic components of Examples 1 and 2 and Comparative Example 1.

In the ceramic component of Example 1, the side surface electrodes were made of an Ag paste containing elemental K-containing glass frit with 0.45 wt. % of the elemental K content in the Ag paste. The end surface electrodes were made of an Ag paste containing an elemental K-containing glass frit with 0.225 wt. % of the elemental K content in the Ag paste. These Ag pastes were applied onto the side and end surfaces, respectively, then dried, and baked at 700° C. for 6 minutes (temperature rise rate: 30° C./min).